Electric valve control circuit



Aug. 4, 1942. J. STRATTON ELECTRIC VALVE CONTROL CIRCUIT Filed Feb. 24, 1941 VQLTAGE ADJUSTING RH sosrxr 7 FAN LOAD: D cam: MOTOR T m o TE H R E mm H L we L E GO RT R R TT U L C 0 A VC IV.

SENSITIVITY; ADJUSTMENT CURRENT ADJUSTING RHEOSTAT m y It t n mmw Mama V A Tm W s e v/ b CURRENT THROUGH WINDING 9 GRID VOLTAGE SATURATION Patented Aug. 4, 1942 2,292,173 ELECTRIC VALVE CONTROL CIRCUIT Jerry L. Stratton, Schenectady,

General Electric Company,

New York N. Y., assignor to a corporation oi Application February 24, 1941, Serial No. 380,228

14 Claims. (01. iu -zzs) My invention relates to electric valve control circuits and more particularly to electric valve systems for precisely energizing a load circuit in response to a predetermined controlling influence, such as voltage or current. I

Electric valve equipment for electronic discharge apparatus has found an expanding field of application in the control of dynamo-electric machines and in the control of electrical conditions, such as voltage and current, of associated load circuits. In accordance with the teachings of my invention described hereinafter, I provide a new and improved electric control system which afiords greater precision in control and operation than, that provided by the prior art arrangements.

It is an object of my invention to provide a new and improved electric control and regulating system.

It is another object of myinvention to provide va new and improved electric valve control system.

It is a further object of my invention to provide a new and improved electric valve. regulating system for dynamo-electric machines.

Briefly stated, in the illustrated embodiment of my invention '1 provide an improvement in electric regulating systems of the type broadly disclosed and claimed in my copending patent application Serial No. 380,227, filed concurrently herewith, and which is assigned to the assignee of the present application More particularly, my improved regulating system relates to an electric valve. regulating circuit or apparatus employing electric discharge means wherein the current transmitted through a load circuit, such as the control or field winding of a dynamo-electric machine, is precisely controlled to maintain an electrical condition of an associated circuit or electrical apparatus at a definite predetermined value. The system includes an electronic amplifier in which means are provided forproducing a positive feed-back voltage which cooperates with the control voltage to increase the sensitivity of the amplifier, but which does not ntroduce the feed-back effect-until the current change has been effected. For example, the means for introducing the feed-back voltage may comprise a resistance connected in series relation with the load circuit and produces the positive feed-back voltage only after the current through the loadcircuit has increased. Other means are provided for adjusting or compensating the operation of the amplifier for variations For a better understanding of my invention, reference may be had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims. Fig. 1 diagrammatically illustrates an embodiment of my invention as applied to a regulating system for controlling the output voltage of a direct current generator and which includes an electronic amplifier and a loaded counter E. M. F. motor which control the field energization of the generator. Fig. 2 represents certain operating characteristics of the electronic amplifier.

Referring now to Fig. 1 of the accompanying drawing, I have there illustrated my' invention as applied to an electric regulating system for controlling an'operating or an electrical condition, such as the output voltage, of a direct current generator i comprising an armature winding 2, a field winding 3 and a commutating winding 4. As a means for controlling the current transmitted to the field winding 3, I employ suitable control apparatus such as a loaded counter E. M. F. motor 5 having an armature 8 and field windings l, B and 9. Field windings I and I may be connected in series relation, as illustrated, across the armature or load circuit of the generator l. Furthermore, the field winding 9 may be arranged to produce a magnetomotive force which opposes the combined effect of the field windings 1 and 8 and may be proportioned to have a magnetomotive force which is less than the combined magnetomotive forces of windings I and 8. By variably energizing winding 8, the excitation of the counter E. M. F. motor 5 is controlled and, hence, the field winding 3 ofgenerator is variably energized. A generator field rheostat 10 may be connected in series relation with the armature t of motor 5 and field winding 3. Generator I may be employed in a system for charging a battery I I, and a suitable circuit controlling means such as a switch 12 may be connected in series relation with thearmature 2 of generator I.

I provide an electronic amplifier H for variably energizing the field winding 0 of motor I in response to a predetermined electrical condition such as the armature voltage of generator I, or the voltage of the-load circuit, to maintain the voltage constant. The electronic amplifier It comprises a source of direct current including a positive conductor I4 and a negative conductor l5 and may be supplied by a rectifier ll, of the bi-phase type, energized from a suitable source in magnitude of the direct current supply voltage. of alternating current. The rectifier It may comprise a transformer I1 and an electric valve II. Primary winding II of the transformer Il may be provided with taps II and II and a switch )2 in order to control the magnitude oi. the voltage or the direct current source comprising conductors II and II. II desired. a suitable filter circuit may be connected between the rectifier II and the amplifier II. and this filter circuit may comprise an inductance II and a capacitance II connected in the manner indicated. It is to be understood. of course. that other suitable filter equipment may be employed.

Electronic amplifier II includes an electronic electrical condition of the associated equipment.

such as the armature voltage of generator 'I or thevoltageoitheloadcircuit,lprovide asecond electronic discharge device II. also preferably oithehighvacuumtypawhichisconnectedui series relation with a suitable impedance element such as a'resistance II. Electronic discharge device II transmits variable amounts current thromh resistance II and. hence, controls the potential oi 'the grid II. Electronic discharge device II comprises an anode II, a cathode II. a cathode heating element II and may comprise control means such as a control grid II, a screen grid and a suppressor grid II which is preferably connected to the oathode II.

In order to impress on the control means, such as the control grid II. a potential which varies in accordance with the output voltage or generator I or the load voltage. I provide a circuit including resistances II. II and II which are connected from the positive terminal of the load Resistanu II may be provided with an adjustable contact II which is connected to the I provide means tor impressing on the discharge device II a positive teed-beck voltage hich is determined or controlled the inductance of the field winduently, the teed-back eflect is not shown in Fig. 2. As an agencyv for controlling the operationoi the electronic amplifier II in order to compensate ior undesirable variations in the magnitude of the voltage appearing across conductors II 7 and II, due to variations in the voltage oi transformer II or due to variations in the power transmitted through the rectifier II. I provide means for varying the potential of the control means. such as screen grid II, in response to variations in the voltage 0! the source.

means may comprise a voltage divider, including resistances II and II, which are connected in series relation with the upper portion of the current adjusting rheostat II across the direct current source. In this manner, a predetermined component or the voltage of the source is impressed on the screen grid II to compensate the operation oi discharge device II for variations in the voltage of the source. As a further means for compensating the operation of the discharge device II for variations in the magnitude of the source. I provide means tor variably energizing the cathode heating element II in response to the voltage of the source. The cathode heating element II may be connected across the source through resistances II and II and a portion or resistance II. In this manner. the temperature of the cathode I2 and hence the anodecathodecurrentvariesinamannertocoinpensate i'or variations in the anode-cathode voltage or the voltage of the direct current source.

The current adjusting rheostat II is employed to control the maximum value oi current transmitted to the load circuit by limiting the maximum voltage diil'erence between the control means, such as control gridjI. and cathode II. This operation may be effected by employing a suitable current responsive means, such as a relay II having a plunger II, an actuating coil II. movable contacts II and II and stationary cmtacts II. II and II. A suitable shunt II may be connectedin series relation with the load'circuit to provide a voltage which is proportional to the current and which eflects energization of the actuating coil II to move the plunger downwardly when the load current attains a predetermined value. the movable contactsbeing biased tothepositionshownbythespringme'ans.

The operation of the embodiment of my inventionshowninl'ig. 1 willbe-esplainedbyconsideringthesystemwhenitisoperatingtomaintaintheloadvoltagaortbevoltagennpre-ed acrosstheterminalsoithebattery II,ataconstant value. Variable smoimts oi current are transmittedtothefieldwindingloigeneratcel byvirtueoitheoperationoithecoimtermlr. motor I. It will be appreciated that as the resultant or net excitation oi the generator I varies.thecounterm.ll.l".oithemotorlopposm theterminaiorarmaturevoltageoigeneratosi invaryinsamountstocontroltheresultantfieid current through windingI. That is. as the net or resultant excitation oi motor I increasm. the counter-nul'koithemotorl incresseseflectingadecresseinthefieldcurrent through winding I. conversely. a decrease inthenetexcitationotmotorlwiiicausesn increase in the field current through'winding I. WindingIopposesineflectwindingsland 'Io'imotorlsothatanincreaseinenergi-tiim of winding I decreases the net or resultant escitation or motor I. and a decrease in the energiaation a winding I increases the net excitation or motor I.

Hectronic regulator II transmits variable amounts or current to field winding I of motor I to maintain the output voltage or armature voltage of generator I at a constant value. Variations in the load voltage or armature voltage are impressed on control grid 94 of electronic discharge device 29 to transmit variable amounts of current through resistances 90 and thus to impress a variabl control potential on grid 28 of discharge device 25. The latter discharge device transmits variable amounts of unidirectional current to field winding 9 from the direct current source includin conductors l4 and I5. For example, if it be assumed that the load voltage tends to rise above a predetermined value, the potential of grid 24 is raised causing discharge device 29 to transmit a larger amount of current and effecting thereby a decrease in potential impressed on grid 29 of electronic discharge device 25. Accordingly, the current transmitted to field winding 9 is decreased, efiecting an increase in the net or resultant excitation of motor 5 and causing its armature voltage or counter E. M. F. to increase. Because of the increase in counter E. M. F., the current through field winding 9 will be decreased, tending to restore the generator armature voltage to the desired value. Of course, if the load voltage tends'to decrease below the desired value, the reverse operation will take place to raise the generator armature voltage to the desired value. The potential impressed on control grid 24 for small variations thereof effects substantial changes in the conductivity of electronic discharge device .29 and causes correspondingly great or abrupt changes in the current conducted by discharge device 25. The voltage adlusting rheostat 99 may be proportioned or ad- Justed so that the discharge device 29 is changed in its operation from cut-oil? to the saturated region, or vice versa, for small changes in the magnitude of the voltage impressed between control grid 94 and cathode 92, thereby eiiecting corresponding abrupt changes in the conductivity of discharge device 22 and rapid changes in current transmitted through control or field winding 9 of motor 5. By means of the positive feed-back voltage derived from resistance 49, the rapid or abrupt change from cut-off to saturation, or vice versa, of discharge device 29 is accelerated. This feature of Operation of the electronic amplifier I9 may be more fully appreciated by referring to the operating characteristics shown in Fig. 2. The heavy curve A represents the current through the control winding 9 as .a function of the voltage impressed on grid 94 of discharge device 29. Curve B represents the ordinary anode-cathode currentgrid voltage characteristic of discharge device 29 having a cut-off characteristic which is relatively sharp. The centralportion of curve A may be made to have a substantially horizontal relationship to obtain abrupt change from cutoff to saturation by adjustment of resistance 49. By decreasing the magnitude of the resistance 49 to decrease the reed-back voltage impressed between cathode 92 and control grid 94, the rate of response or the rate of change of the current through winding 9 may be adjusted to assume values corresponding'to'the dotted curves 0, b, c or d. As'the magnitude of the feedback voltage is decreased by decreasing the value of resistance 49, the central portion of curve A approaches as alimit the portion of the grid voltage characteristic curve B lying between cutoff and saturation. In this manner, the sensitivity and speed of response of the amplifier H for variations in load voltage may be controlled or adjusted.

When the relay 41 is in the position shown in the drawing, the circuit through which the feed-back voltage is eirective includes resistance 49, the lower portion of the current-adjusting rheostat 45, contacts 59 of relay 41, battery H, resistance 91, the right-hand portion of resistance 38, battery 4|, resistance 42, and g d 94 and cathode 92 of discharge device 29. When the relay 41 is in the energized position corresponding to the current-control position, the circuit through which the feed-back voltage is effective includes resistance 49, the lower portion of the current-adjusting rheostat 45, contacts 54 ofrelay 41, shunt 55, contacts 52 of relay 41, grid 34 and cathode 32 of discharge device 29.

An important advantage of apparatus built in accordance with my invention, particularly as applied to the control of a load circuit having an appreciable inductance such as the field winding of a dynamo-electric machine, is the manner in which the variation in current through the load circuit may be employed as a damping circuit, that is, as a damping control with respect to the time of application of the feedback voltage. Referring particularly to the anode-cathode circuit of the electronic discharge device 25 which is connected in series relation with field winding 9 and resistance 49, the feedback voltage'does not become efiective until the current change has taken place. This is true because the voltage drop across resistance 49 does not change until the current has chan ed. Consequently, the change in feed-back vol e does not become eflective until the current has changed. In this manner, the system operates without appreciable hunting by utilizing the characteristic ofthe load circuit in conjunction with the positive feed-back feature.

Amplifier l 3 operates to maintain precisely the voltage of the load circuit irrespective of variations in the magnitude of the direct current source including conductors l4 and I5- Th s control is obtained by impressing on the screen rid 95 a voltage which compensates the operation of the discharge device 29 and, hence, corrects the operation of the amplifier I9 for variations in the voltage of the direct current source. For example, were it not for this compensating feature, the magnitude of the load voltage which is maintained by the system would vary with the voltage of the source.' If the voltage of the source tends to rise, the potential impressed on screen grid 95 correspondingly rises effecting a lowering in potential of grid 28 of discharge device 25, thereby decreasing thepotential of grid 29 to compensate for the increase in anodecathode voltage of this discharge device so that the same value of current is transmitted to field winding 9 for a definite value of load voltage. The amplifier circuit I9 is also additionally compensated for variations'in the direct current source by variably energizing the cathode heating element 99 in response to the voltage of the source. Ifthe voltage tends to vary from the desired value, the current transmitted to the cathode heating element 99 will also be varied to change the temperature of the cathode 92, thereby changing the current conducted by the discharge device 29' to raise or lower the potential of grid 29 of electronic discharge device 25 so that the same value of current is transmitted to winding 9- for a definite signal "or control voltage derived from the load circuit.

By means of resistance 38, the output voltage of the generator I orthe load voltage may be controlled or adjusted. Through the operation of the relay 1, if the load current tends to increase above a predetermined value the electronic ampli- .fier I3 is controlled to maintain constant load currenti This operation is effected in the following manner. Upon increase of load current to a predetermined value, actuating coil 49 of relay 41 is sufliciently energized, pulling the plunger 48 downwardly to close contact 52 and 54. As a result, battery I is shunted through resistance and contacts 52 of relay 1, thereby rendering inefi'ective the reference voltage of this battery.

Upon closure of contacts 52 and 54 of relay 41, variable amounts of unidirectional current are transmitted from shunt 55 through the lower portion of resistance 46 and resistance 43 in response to the current transmitted by the load circuit. When contacts 52 and 54 of relay 4'! close, battery 4| and resistances ill-39 are effectively shunted so that the control effect is produced exclusively by the voltage variation appearing across the terminals of shunt 55. If the current tends to rise above the predetermined value, the control grid 3! of discharge device 29 i raised in the positive direction to transmit a corresponding amount of current through resistance 30 and consequently efiects a lowering in potential of grid 28. Accordingly, the current transmitted to field winding 9 is decreased, causing an increase in the resultant excitation of the counter E. M. F. motor 5. This increase in excitation increase the counter E. M. F. of the motor and decreases the excitation of generator I, thereby restoring the current to the desired value. Of course, the system operates to maintain the load current. constant irrespective of any tendency oi the load current to vary in either direction.

While I have shown and described my invention as applied to particular systems 01 connections and as embodying various devices diagrammatically shown, it will be obvious to those skilled in the art that changes and modifications may be made without departing from my invention, and

I, therefore, aim in the appended claims to cover allsuch changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a dynamo-electric machine having a control winding, a source of direct current comprising positive and negative conductors, an electronic discharge device, having a grid, connected to transmit variable amounts or unidirectional current through said control winding, a serially connected resistance and a second electronic discharge device energized from said direct current circuit for impressing a variable control potential on said grid, said second electronic discharge device having an anode, a cathode and a control grid, and feed-back means responsive to the current transmitted through said control winding to impress a positive feed-back voltage between said cathode and grid of said discharge device.

2. In combination. a. dynamo-electric machine having a control winding. a source of direct current comprising a positive conductor and a negative conductor, an electronic discharge device, having a grid, connected to transmit variable amounts of unidirectional current through said control winding, a serially connected resistance and a second electronic discharge device energized from said direct current circuit for impressing a variable control potential on said grid, said second electronic discharge device having a control grid, and feed-back means comprising a resistance connected in series relation with the first mentioned discharge device and said control winding for impressing a positive teed-back voltage on the grid 01 said second discharge device.

3. In combination, a dynamo-electric machine having a control winding, a direct current circuit having positive and negative conductors, an electronic discharge device energized from said direct current circuit for transmitting variable amounts of unidirectional current through said control winding, said discharge device having a grid, means energized from said direct current circuit and comprisin a serially connected resistance and a second electronic discharge device for impressing a, variable control potential on said grid. said second electronic discharge device comprising an anode, a cathode and a pair of control grids, means for impressing on one of said pair of control grids a voltage which varies in accordance with a predetermined controlling influence. feed-back means connected in series relation with the first mentioned discharge device and said control windin for impressing a positive feedback voltage on said second discharge device in response to the flow of current through said control winding, and means connected across said source for impressing on the other control grid a voltage to compensate the operation of said second discharge device for variations in the voltage of said direct current circuit.

4. In combination, a dynamo-electric machine having a control winding, a direct current circuit having positive and negative conductors, an electronic discharge device energized from said direct current circuit for transmitting variable amounts oi unidirectional current through said control winding, said discharge device having a grid, means energized from said direct current circuit and comprising a serially connected resistance and a second electronic discharge device for impressin a variable control potential on said grid, said second discharge device comprising an anode, a cathode and a pair oi control grids, means responsive to a predetermined controlling infiuence for varying the potential oi one 01' said pair of control grids, means responsive to a second predetermined controlling influence for varying the potential on said one grid, means connected across said direct current circuit for varying the potential of the other of said pair oi grids to compensate the operation of said second discharge device for variations in the voltage of said direct current circuit, and means responsive to the current transmitted through said control winding for impressing on one of said pair of grids a positive feed-back voltage.

5. In combination, a dynamo-electric machine having a control winding, a direct current circuit having positive and negative conductors, an electronic discharge device energized from said direct current circuit for transmitting variable amounts oi unidirectional current through said control winding, said discharge device having a grid, means energized from said direct current circuit and comprising a serially connected resistance and a second electronic discharge device for impressing a variable control potential on said the last mentioned voltage in response to the cur-" rent transmitted through said resistance, means for impressing on the other of said pair of grids a voltage to compensate for variations in the magnitude of the voltage of said direct current circuit, and feed-back means connected in series relation with the first mentioned discharge device and said control winding for impressing on one of said pair of grids a positive feed-back voltage.

6. In combination, a direct current circuit, a load circuit, electric apparatus for controlling the energization of said load circuit comprising a dynamo-electric machine having a control winding, a'source of direct current, an electronic discharge device, having a grid, energized from said source for transmitting variable amounts of unidirectional current through said control winding, means energized from said source and comprising a serially connected resistance and asecond electronic discharge device for impressing a variable control potential on said grid, said second electronic discharge device comprising an anode, a cathode and a pair of control grids, means for impressing on one of said pair of control grids a voltage which varies in response to the voltage of said direct current load circuit, means comprising a voltage divider connected across said source for impressing on they other means a positive feed-back voltage' to increase the sensitivity of said second discharge device grid of said pair of grids a voltage to compensate the operation of said second discharge device for variations in the magnitude of the voltage of said source, and feed-back means responsive to the current transmitted through said control winding for impressing a positive feed-back voltage on one of said pair of grids.

'7. In combination, a direct current circuit, a load circuit, means for energizing said load circuit from said direct current circuit comprising an electronic discharge device having a grid, means for impressing on said grid a variable potential comprising a serially connected resistance and a second electronic discharge device comprising an anode, a, cathode, a cathode heating element and control means, means for impressing on said control means a variable voltage to control the energization of said load circuit, means responsive to the current transmitted through said load circuit for impressing a. positive feedback voltage on said control means, and means for variably energizing said cathode heating element in response tothe voltage of said direct current circuit thereby compensating the operation of said second electronic discharge device for variations in the magnitude of the voltage of said direct current circuit. I

8. In combination, a direct current circuit, a load circuit, means for energizing said load circuit from said direct current circuit comprising an electronic discharge device having a grid, means for impressing'on said grid a variable potential comprising a serially connected resistance and a second electronic discharge devicecomprising an anode, a cathode, a cathode heating element and a control means, means for impressing on said control means a control voltage varia resistance connected in series relation with said load circuit for impressing on said control with respect to variations in said control voltage, and means for variably energizji'ii'gsaid cathode heating element in response to the voltage of said direct current circuit. I a

9. In combination, a direct current circuit, a load circuit, means for variably energizing said load circuit comprising an electronic discharge device having -agrid, means for impressing a variablefltrol'fpotential on said grid to control the amountioficurrent,transmitted to said load circuit comprising a serially connected resistance and a secondelctroniqdischarge device comprisingan iincdeya cathode, a cathode heating e1ement;a:eontrol grid and a screen grid, means for impressiifii'onsaid control grid a potential which variesin accordance with a predetermined I controlling influence, feed-back means for impressing on said control grid a positive feed-back voltage infre'sponse to'th'ecurrent transmitted through said; -load circuit, means comprising a voltage divide or nected across said direct current-circuit for impressing on said screen grid a voltage proportional to the voltage of said direct current4circjuit thereby compensating the operation of 'said seemedischarge device for variations in the magnitude of the voltage of said direct current circuit, and means for variably energizing said cathode heating element in response to the magnitude of said direct current circuit.

10. In combination, a direct current load circuit, means for controlling the energization of said load circuit comprising a dynamo-electric machine having a control winding, apparatus for variably energizing said control winding comprising a source of direct current, an electronic discharge device having a, grid for transmitting variable amounts of unidirectional current through said control winding from said source, mean for impressing on said grid a variable control potential comprising a serially connected resistance and a second electronic discharge device comprising an anode, a cathode, a cathode heating element, a control grid and a screen grid, means forimpressing on said control grid a voltage which varies in response to the voltage of said direct current load circuit, means for impressing on said control grid a positive feed-back voltage in response to the current transmitted through said control winding, means comprising a voltage divider connected across said source for impressing a compensating voltage on said screen grid, means for variably energizing said cathode heating element in response to the voltage of said source, and means connected between said direct current load circuit and said control grid for varying the volt age of said control grid to maintain constant the current of said direct current load circuit.

11. In combination, a direct current load circuit, means for controlling the energization of said load circuit comprising a dynamo-electric machine having a control winding, apparatus for variably energizing said control winding comprising a source of direct current, an electronic discharge device, having a grid, for transmitting variable amounts of unidirectional current through said'control winding from said source, means for impressing on said grid a variable control potential comprising a erially connected resistance and a second electronic discharge device comprising an anode, a cathode, a cathode heating element, a control grid and a screen grid, means for impressing on said control grid a voltage which varies in response to the voltage of said direct current load circuit, means for impressing on said control grid a positive feedback voltage in response to the current transmitted through said control winding, means comprising a voltage divider connected across said source for impressing a compensating voltage on said screen grid. means for variably energiz ing said cathode heatim element in response to the voltage of said source, and means responsive to a predetermined value of current transmitted-by said direct current load circuit for controlling the potential diiierence between said control grid and said cathode to maintain constant current in said load circuit.

12. In combination, a direct current load circuit, means for controlling the energization oi said load circuit comm-hing a dynamo-electric machine having a control winding, apparatus for variably energizing said control winding comprising a source oi direct current, an electronic discharge device, having a grid, ior transmitting variable amounts of unidirectional current through said control winding from said source, means for impressing on said grid a variable control potential comprising a serially connected resistance and a second electronic discharge device comprising an anode, a cathode, a cathode heating element, a control grid and a screen grid, means for impressing on said control grid a voltage which varies in response to the voltage of said load circuit to maintain the voltage of said load circuit at a constant value, mean; for impressing on said control grid a positive feedback voltage in response to the current transmitted through said control winding, and means responsive to load current or a predetermined value for controlling the potential diflerence between said control grid and said cathode thereby maintaining the load current constant.

13. In'combination, a direct current circuit, a load circuit. means for energizing said load circuit from said direct current circuit comprising an electronic discharge device having a grid, means for impressing on said grid a variable potential comprising a serially connected impedance element and a second electronic discharge device comprising an anode, a cathode and control means, means for impressing 'onsaid control means a variable voltage to control the energization of said load circuit, and means responsive to the current transmitted through'said load circuit for impressing a positive iced-back voltage on said control means.

14. In combination, a direct current circuit, an inductive load circuit, means for energizing said load circuit from said direct current circuit comprising an electronic discharge device having a grid. means for impressing on said grid a variable potential comprising a serially connected resistance and a second electronic discharge device comprising an anode, a cathode and control means, control means connected to said control mean and comprising means responsive to a predetermined electrical condition of said load circuit for impressing on said control means a variable voltage to control the energization of said load circuit, and means responsive to the current transmitted through said load circuit for impressing a positive feed-back voltage on said control means, the inductance of said load circuit constituting with said control means a damping circuit.

JERRY L. STRA'I'ION. 

